The present invention, in some embodiments thereof, relates to a system and a method for controlling light intensity reaching a user's retina and, more particularly, but not exclusively, to a system and a method for filtering out blue light (and/or light of a greater wavelength) while keeping overall light intensity reaching a user's eyes below a maximum predetermined value.
Diabetes is a very widespread debilitating disease. In the US alone, over 20 million adults and children (7% of the population) have diabetes, and the rate of diagnosis of both Type 1 and Type 2 diabetes is rising. One of the many manifestations of the body's inability to properly control glucose levels in the blood is degradation of the retina, often leading to blindness. In North America, diabetes is the number one cause of blindness for people under 65 years of age. Diabetic retinopathy is a complication of diabetes mellitus (DM) that progresses slowly from an early background stage to a late and severe vision-threatening stage, Proliferative Diabetic Retinopathy (PDR).
A growing body of evidence indicates that the primary damage in diabetic retina is caused by hyperglycemia, and reflected by impairment in retinal function accompanied by apoptosis of retinal cells. High blood sugar levels can lead to free-radical formation, resulting in damaged blood vessels, including tiny blood vessels in the eye. Such damage leads to diabetic retinopathy. With diabetic retinopathy, some blood vessels in the retina are lost, while others leak blood. The result is a swollen retina that can cut off its supply of oxygen and nutrients. Eventually, the retina can grow new blood vessels to replace the damaged ones. New blood vessels are not as strong as the old ones and are more likely to break, causing bleeding in the eye.
The damage caused by diabetic retinopathy is considered irreversible. Still, there are ways to slow or prevent further damage to the retina. Vitrectomy, or retina-directed laser surgery, is used to seal leaky blood vessels associated with the retina. Additionally, proper insulin use to prevent extended periods of hyperglycemia aids in reducing production of free radicals that cause further eye damage.
In U.S. Pat. Nos. 4,878,748 and 5,617,154, Hoffman describes colored contact lenses that prevent light of wavelengths 200-500 nanometers wavelength from passing through the contact lenses, with light of 500-700 nanometers wavelength having a predetermined level of transmittance. Hoffman describes the UV-associated damage to lens, cornea and retina, as well as its implication in yellow cataracts. He additionally states that blue light is implicated in macular degeneration and retinal damage. People with “special requirements” have an added requirement for protection of UV and blue light.
In U.S. Pat. No. 5,177,509, Johansen and Diffandaffer describe sunglasses that effectively cut out light from 300 nanometer wavelength to a final upper wavelength of 450, 500, 515, 535, or 550 nanometers.
Optiplas (www.optiplas.co.il) offers glasses, with both light and dark tinting, for patients suffering from diabetic retinopathy and macular degeneration. They recommend CPF 527 and CPF 511 cutoffs for lenses for patients demonstrating either of these conditions so as to reduce UV and blue light from reaching the eye.